Oil burner system comprising a vaporizing block



Aug. 17, 1948. -r. H. SMOOT" 2,447,373

I OIL BURNER SYSTEM COMPRISING A VAPORIZING BLOCK Filed May 27, 1944 4 Shg'etS-Sheet 1 T R t Q Q k E R k i g v &\ g Q E? I. a

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T. H. S OTQ Aug. 17, 1948.

QIL BURNER SYSTEI COMPRISING A VAPORIZING BLQCK Filed lay 27, 1944 4 Sheets-S t 3 HIiHi L INV TOR.

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'r. H; SMOOT OIL BURNER SYSTEM COMPRISING A VAPORIZING BLOCK Filed May 27, 1944 4 Sheets-Sheet 4 umq M M n. T m N I I L M8 2 P! w! .m a 7. t H fi M. v. B

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Patented Aug. 17, 1948 OILYBURNER SYSTEM COMPRISING A VAPORIZING BLOCK Theophilus H. Smoot, Baltimore, Md., assignor to Anchor Post Products, Inc., a corporation of New Jersey Application May 27, 1944, Serial No. 537,599

1 r This invention relates to a system of burning oil or other liquid fuel for heating purposes and involves the use of a heat-resistant capillary block with holes running through it to serve as a medium for the vapor entrainment of a liquid fuel. Such a liquid fuel is fed to the block, and air at relatively high velocity is forced through the holes to entrain the fuel in the form of a vapor which is either wet or dry. It is essential that some of the fuel be actually vaporized but I am using the phrase entrained vapor" to cover the case where at least a part is vaporized while a part may be present in the form of minute droplets. v

I realize that a great many attempts have been made to burn'fuel with the aid of a heat-resistant capillary block but I believe that none of these devices has met with any permanent degree of success. By the present invention I aim to produce a burner which employs the capillary block principle in an emcient and commercial manner and this invention is based upon the discovery of what I believe to be the essential factors whereby such a device can be operated efll- If a very low air velocity is used with the block, such as results from the use of natural draft, and relatively large holes are formed in the block, enough oil may be volatilized or entrained to support combustion, and this is particularly true if the block is exposed to the radiant heat of the flame. In such case, carbon is formed on the block but after the oil is burned off the flame will continue for quite a period of time and tend to burn off the carbon residues. with a device of this kind combustion is relatively slow but it has been suggested that the hot face of the block assists combustion by virtue of the socalled surface combustion effect.

when one attempts to increase the air flow in such a device by the use of forced draft there is an immediate loss of efllciency becausethe fuel (except perhaps in the case of an unusual fuel such as arctic gasoline) will not volatilize with sufllcient rapidity. In fact, in such case a substantial increase in the air flow will extinguish the flame.

-I have found that this difllculty can be overcome by carefully avoiding any surface combustion" and by supplying heat to aid in volatilizing the fuel, which is supplied under specialized, controlled conditions. The most efficient way of supplying this heat is to preheat the air which is forced through the block.

Broadly speaking, my invention can be de- 4 Claims. (Cl. 158-28) scribed as an oil burner which includes a heatresistant capillary block with holes running through it and to which liquid fuel is supplied from any convenient source so that it will be absorbed by the block. A fan or other equivalent means is employed for forcing air through the holes in the block and a mechanism such as a heat exchanger is employed for preheating the air which is forced through the holes.

When the air is heated to a temperature within the desired range (as later described), the liquid fuel will be vaporized or entrained with great efllciency, and a mixture of air and vaporized fuel will come out of the holes which is combustible but which is actually over-rich in fuel. To obtain the most emcient combustion, secondary air should be supplied, to be mixed with the primary air and vapor. This secondary air is also preferably heated, and it should be mixed with the primary air and vapor in such a way that entrained droplets will not strike the walls of the device until combustion has proceeded far enough substantially to prevent the deposition of carbon. I

As regards the temperature to which the air should be preheated, this will depend in part upon the nature of the fuel. With a fuel such as ordinary motor gasoline, preheating cold outdoor air from zero or below to F. will show a marked benefit, though even with this type of fuel the temperature should preferably be above F. With a heavier fuel such as kerosene or a #2 fuel oil such as is ordinarily employed with domestic oil burners, a higher temperature is needed and this temperature preferably should not be below about 200 F. and certainly not below F.

The principal care that must be taken is to see that the temperature does not go too high. All of the hydrocarbon fuels usually employed in oil burners tend to start to decompose at a temperature in the order of about 400 F. and as a general rule this temperature should not be exceeded. In fact with the heavier fuels where the ratio of carbon to hydrogen is higher than in the case of the lighter fuels, there is a tendency 190 F. and 330 F.

this can be done only if the construction of the.

furnace is such that when the furnace is operating efllciently the block will not be heated above 400 F. by the direct furnace heat. To prevent this occurring I have found that certain structural points must be observed.

First of-all, the porous block must not project into an actual combustion chamber. It is obvious that if it does, the temperature in the combustion chamber will be above 400 F. and the block will become too hot.

Even if the principal combustion takes place in a combustion chamber beyond the block. surface combustion should not be permitted to ocour in or around the block. This can be prevented by providing a covering for the block largely enclosing such block except for the surfaces through which the air passages run. This prevents combustion taking place around the periphery of the block, and combustion within the block is prevented by forcing the air through the passages at a suificient velocity so that flashback into the passages is prevented. It is advisable to provide a zone beyond the block, which may be termed the mixing zone, into which the air and volatilized fuel is discharged from the passages into this zone secondary air at points removed from the face of the block. This mixing zone opens into a combustion chamber and by this arrangement the combustion. against the face of the block is further prevented.

Actually I have foundthat the high velocity of the air forced through the passages in the block very largely reduces thestatic pressure on the walls of these passages and there is a tendency for the vapor to move toward the passages from those portions of the block which are subjected to normal static pressure. Even the exposed face of the block which is directed toward the flame will be subject to a static pressure approaching normal so that virtually no vapor will permeate this part the block will-stay clean even though at which one would expect carbon to be-deposited. A'capiilary block of the type employed (which is ordinarily made of ceramic material) is anextremeiy poor heat conductor and excess heat will not penetrate far enough into the block .to do any harm. but it is preferable to have the exits from the es belied-out so that the reduced pressure caused, bythe air velocity will not tend to draw vapor into those portions of the block around the outlet orifices.

It is an interesting fact that my device can even be used as'an'eflicient mechanism for burning fuels to supply a shield between the outlet face of the block and the flame, and to supply tubes running from the ends of the air passages,

through the shield. Such a shield-may for example be made of a low density material such and to provide means for introducing of the block. As a result its exp sed face does reach a temperature higher than thatblock will absorb the fuel in .offueltothe when once carbon starts -to keep the heating of the block warms up,

as an insulation refractory. which may be supplied with metal-lined air and vapor passages.

Even though some of the heat (if properly controlled) may be supplied to the block by direct radiation, it is advisable to have the combustion air (and particularly the air used for entraining vapors) preheated to a temperature at least slightly higher than the average temperature of the block during operating conditions. Heat units must be supplied for vaporization, and if the air is colder than the block temperature, there will be a tendency for the air to cause condensation to take place either on the face of the passages or in the air stream, with the formation of fuel droplets which may not be properly consumed. The preheated combustion air maintains the entrained fuel in the form of I a vapor in its travel from the place of entrainment to the place of combustion because of the available heat in the preheated combustion air as contrasted with entraining. vapor in cold air. In the latter case. the vapor would give up heat to the air and there would consequently be a greater tendency for condensation to take place. In view of this fact, I have found it desirable I block by radiation down to a minimum and torely upon the preheating of the air to supply the heat units for maintaining the block at the desired temperature and for supplying the additional heatunits necessary for vaporization.

The combustion air may be preheated to the desired temperature either as a functionaof the design of the heat exchanger while passing all of the combustion air through it. or the heat exchanger may be designed to raise the temperature of a part of the combustion air above the-desired point, and this airmay be mixed with colder air to give the necessary temperature control. useful for quick starting under conditions of extreme cold, as'the hot air alone can beused duringthe initial combustion and then as the colder air can be blended in to give the desired temperature during operation. When theburner is shut off, residual fuel will remain in the block-for a short time. Accordin ly. it is desirable to so arrange the device that the flow of air will-continue for a time after the blockhas been stopped. This expedient is ordinarily suflicient when working with gasoline but when working with a heavy oil such as #2 fin-pace oil, the capillary block may be in a relatively wet condition when the fuel fed to the burner is stopped. In such case. the block will continue to produce vapors at a decreasing rate as the -flre dies down. Finally a point is reached at which-the vapors entrained in the air stream are not sufficient in amount to maintain a combustible mixture and the fire goes out. However, this will occur before all the vapors have been driven off and as the still warniair is passed through the block an odor may be produced at the exhaust. This can be stopped by providing mechanism so thatat a predetermined time after the flow of fuel to the block is cut off. cold air is turned through the block which will rapidly reduce the volatiiization of the. fuel and exceramic material. The holes through the block a This last arrangement is particularly may be located only in the upper part particularly if bottom feed is used; formly through the block where another arrangement for fuel introduction is used. These holes should be small enough so that the air passing through them will have sumcient velocity to prevent the flame from working back into the holes. For example, a burner of 100,000 B. t. u. per hour rated capacity will be large enough to heat an average well-built house of about 12 rooms. For such a burner the block can be a disk about 3 inches in diameter andabcut one-inch thick and theholes in the upper part can be about 1% inches in diameter. In one case I employed 1'7 holes of this size. These figures are given only as an indication of desirable proportions and not in any way as a limitation.

Preheated air is forced through the holes by any convenient mechanism such as a fan, and a part of the preheated air will preferably pass around the outside of the block to serve as secondary combustion air. In order to prevent combustion from taking place adjacent the outer peripheral surfaces. which might lead to the block. becoming too'hot, the block is preferably encased in metal or othersubstantlally impervious cover.

or may be distributed uni If desired, a thin layer of air can be brought 7 around the surface of the block, but in such case this layer should be caused to moveat su fllcient velocity to prevent the propagation of flame from reaching back around the sides of the block. If the block is subject to direct impingement of the flame, control is virtually impossible.

,When using a volatile fuel such as gasoline I find it advisable to form the passages through the block. in the upper part of the block and enclose the lower part of the block in a liquid-tight container. In such case the liquid fuel may be introduced into the block within this container and a safety device can be used so that the liquid fuel can never rise high enough to enter the fuel passages except as theme! is absorbedand subsequently vaporized. With heavier types of fuel where vaporization is slower, this may lead to an unduly large absorption of fuel by the block and in such case it is sometimes advisable to feed the fuel into the top of the block but to control the amount of fuel admitted so that it is vaporized and consumed at the same rate it enters the block.

An igniter of proper design is used to initiate combustion when the device is first put into operation. With a light and volatile fuel I prefer to use a hot wire type of igniter, which may be located either inside or on the combustion face of the block. With a less volatile fuel satisfactory results can be had with a spark igniter. T

.A device utilizing the principles of this invention can be built very light in weight and relatively inexpensively, as it needs no moving parts except the fan for forcing the air through the heat exchanger and through the carbureting block, and in some cases, such as airplane and automatic heaters, this same fan can advantageously be employed for; moving the air that is to transmit the heat to the point of application.

It will also be found that one of the great meritsof the device of this invention is its extraordinary range of modulation. It will operate emciently for an unbelievably large variation in the amount of fuel consumed provided the supply of com-I bustion air is adjusted proportionately.

In an ordinary oil burner unless the size of the nozzle is altered, a variation of 10% plus or minus in the amount of fuel consumed will usually be 6 the absolute maximum within the range of reasonable efllciency. With a structure made in accordance with my invention I have found that a given device can be operated over a range of from /z-pint of fuel up to 5 gallons of fuel per hour, which is an increase from minimum to maximum of 8000%. Of course if a burner capable of handling 5 gallons of fuel per hour is operated on the .basis of only l z-pint per hour, the flame is not much more than a pilot light. but nevertheless such alight can be maintained with reasonably good combustion characteristics. Naturally if the amount of oil supplied to the burner'is varied, the amount of air must also be varied but it isa very simple mechanical matter to control the supply of fuel and the supply of air by common mechanism so that they will be kept properly proportioned. In this way wide modulation in the amount of fuel consumed can be had without undue loss of emciency.

The light weight with which the device can be built and the ability to modulate the amount of fuel consumed both are factors which make this device emcient for use as a heater to be employed in airplanes. With the larger planes it is desirable to have them warmed before the flight starts, but ordinarily. much more heat is needed when a plane is subjected to heavy wind pressures at the intense cold of high altitudes as compared to that which is needed on the ground. My device readily lends itself to such a change and I have found that I can arrange to have this change made automatically. If the plane is to be heated before the flight, then while it is on'the ground the air for both combustion and for convection heating may be supplied by a fan. This fan has its inlet connected to a. pressure-ram or scoop. Under ground conditions when this fan is in operation the inlet to the fan will show a slight negative pressure relative to the surrounding air. When the plane is in flight the pressure-ram or scoop supplies more air than that drawn by the fan, and therefore pressure will be built up in the, inlet, and pressure mechanism connected to this point can be employed automatically to turn off the fan and to operate a device for increasing the supply of fuel fed to the vaporizer. The increased quantity of air picked up by the pressureram then passes through the fan blades and through the rest of the device. Proper barometric controls may also be supplied in the combustion air line so that as the air" rarefies at higher altitudes, the combustion air passage will open to maintain acontrolled weight of air in the burner supply.

When operating the device as a fixed installation (as for heating buildings, ovensor the like) these particular controls will not be necessary but thermostatic or other mechanism can be employed to vary the amounts of air and fuel to be supplied to the burner as conditions may demand.

When light fuel is employed it is possible that the fuel will he actually vaporized. With heavier fuel part may be converted into vapor and also all or part of the fuel may be picked up from the surface of the holes through the block in the form of minute droplets. Even though these droplets are not theoretically vaporized nevertheless I am using the word "vaporized" ascovering the conversion of the liquid into a gaseous form as illustrated by either type of operation.

This invention can readily be understood from the accompanying drawings 'which illustrate a form of device as embodied in. a heater designed for use in airplanes. In these drawings Fig. lis a sectional side view of the device; Fig. 2 is a view of the left hand end of the device as viewed in Pig. -1;" 8 is a sectional detail through the capillary .block showing the fuel'feed and the igniter; P13. 4 is the line 4-4 of Fig. 1; Fig. 5 is a vertical section through the absorbing unit and mixing chamber; Fig. 8is a section on line 4-4 of Fig. 5; Fig. 'l is a section on line 1-4 of Fig. 1; Fig- 8 is an end view of the right hand end of the device as viewed in Fig. 1; Fig. 9 is a view of the outside of the device taken from the oppostie side from that shown in showing the operation of the controls of the mechanism.

I pass freely under flight conditions; This blower a sectional plan view taken on Fig. 1; and Fig. 10 is awiring diagram These drawings were made from a burner of 90,000 B. t. u. per hour rated capacity which if utilised in an ordinary well-built house would be large enough to heat an average house of twelve rooms. In the drawings the numeral ll designates the porous refractory element and for this purpose a ceramic of high porosity is advisable. In order that the scale of the drawings may be appreciated this ceramic block in the device of the size specified was 3" in diameter. As here shown the block or element II is in the form of a section from a cylinder with a number of relatively small holes I! passing throughit in-its upper half. This element is enclosed in a casing l4 which on one side covers the entire face except that holes are formed through it which register with the holes if. Onthe other face as indicated in Fig. 6 there is a semi-circular opening which exposes all of the holes I! and the face of the block between these holes. The pipe l4 inducts the fuel into the block II where it is absorbed. The pipe II is screwed tightly into the casing 14 so as to make a liquid tight joint in order that if any of the fuel delivered to the block I0 is not absorbed it will not run out into the device.

In order to provide a mixing chamber for the vaporized fuel and air a ring I1 is provided run,-

ning out from the casing M. In the periphery of the ring l1 are positioned vane-like members it which are slotted to admit secondary air to the point of combustion. An annular plate 20, which may be. provided wlth'a secondary plate 22, serves to provide an orifice through which the flame emerges.

The parts thus far described are supported in a cylindrical casing 24 by wing members 24 (see Figs. 5 and 6). The casing 24 forms the main combustion chamber and is provided with exterior fins as indicated at 28 in order that the heat generated 'in this combustion chamber may be readily absorbed by the convection air which passes around outside of it and is used to heat the plane.

As shown in Fig, 1 the products of combustion from the main combustion chamber within the casing 34 pass downwardly through the passage 34 which opens (as indicated in Fig. 7) into the oil-center hole-82 formed in one end of the oval fins 41 to assist in heating theconvection air.

Both the convection air and the combustion air are supplied by the blower 38 which is electrically driven when the plane is on the ground but is provided with vanes through which the air can is shown in Fig. 1 without any air connection to the air inlet, but'this connection is indicated in Fig. 2 by the numeral 40. This connection is intended to run to a source (ordinarily supplied as part of the ventilating system of large airplanes) which will carry air at slightly superatinospheric pressure when the plane is in flight.

It is intended that about twice as much air will be supplied during flight as when grounded.

The air for combustion is withdrawn from the central part of the blower 34 and passes upwardly through a pipe 40 and then over and down through the pipe 41 and runs toward the combustion end of the device through pipe 44 which longitudinally within the 'ovalt'ube 84 (see Fig.1). In this figure it is to be noted that the member marked as 44 is a tube running within the casing 84 whereas the ring indicated by the numeral 34 is not a tube through the casing 34 but is the opening for the combustion gas outlet which is shown more clearly'in Fig. 1. The hot combustion gases pass through the tube .84and the pipe 44 within this tubeis exposed to the heat of the products of combustion and therebfythis pipe and the combustion air heated. In this device the parts are so designed that the air in the tube 44 is heated under normal operation toa' temperature of approximately 300" P.

The heated air from the tube 44 passes upto enter the mixing chamber through the va'nelike members It to supply the necessary secondair. It is to be noted that the casing l4 surrbu'nds the 'outside periphery of the'block ll so that while this secondary air helps to heat the block, combustion around the periphery of the hlo'ck'is prevented.

Convection air from the blower II enters the outside casing 48 and'is heated by the this and 3] as well as by the surfaces of the combustion. chamber 24 and the oval tube .34, emer through the passage so to be piped to the points where it is tohe released and employed. Most of the parts of this device are made of sheet metal. It is understood that those parts which are to be exposed to high temperatures preferably are made of a heat-resistant chromium steel allflye fuel feed is illustrated in a. The fuel islntroduced by a' pipe 54 to a pump 54 (which may be of any desired type such as a gear pump ora bellows or diaphragm type of pump) driven through gearing indicated at It by a variable speed motor 00. From the pump 45 fuel passes through the tube 42 to a float valve 44. which is so arrangedthat it'will close if the level of the fuel in the casing l4' rises high enough to wet the surfaces of the es i2. Tube 40 runs from the pump 40 to a pressure switch 00 which will control the operation of the motor 40 if the pressure rises too high. Ordinarily the amount of fuel fed to the block it will be so proportioned to the combustion that it will be absorbed as soon as it reaches the block, so that no liquid will collect withinis in flight as is supplied to it when the plane is grounded. The member'designated by the numeral To is a conduit for conducting electric current from the junction box I2 to the igniter. Member E3 is a static pressure tube to communicate the pressure of the combination air at the burner to the barometric control for combustion air.

The igniter here illustrated is positioned in the center of the block as shown in Pig. 3. This igniter has a casing 10 of conductive metal which is attached to the casing 14 by clip 76 and thereby is grounded. Within the casing I4 is an insu'lating mass 16 through which passes a screw 18 which is locked on the outside of the casing M by a nut 80 and an insulating washer 82. Brazed to the end of the screw 18 is a resistance wire ad which is wound in a spiral about an electrical insulating support 86. The end of the resistance wire is connected to the casing 14 and thereby grounded as indicated at 08. One or more slots are cut in the face of casing 74 as indicated at 90 through which vapors can enter the casing it from the block I0.

When the ignition is turned on, wire 85 becomes hot thereby heating casing It which in turn heats the part of block iii adjacent this casing vaporizing somev of the absorbed fuel. The air passing through the passages I 2 creates some suction at the outlet oi. the casing I4 and draws the warm vapors through the slots 90 into this casing where they are ignited. Theflames from these vapors tend to ignite the vapors that are emerging from the passages i2 and gradually as the device heats up the block i becomes warmed to a temperature of approximately 300 F. at which point com-bustion reaches its maximum efficiency and the igniter can then be turned oil. I have found that this operation usually takes in the order of about 3 minutes and therefore I preferably arrange to have the igniter remain on for about minutes as will be explained hereafter.

Withthis device two timing operations are desirable. One controls the time that the igniter is maintained hot as has just been explained, and the other is the purging operation. When the heater is shut down the supply of fuel should'flrst be shut ofi but the air should operate for an appreciable length of time afterward (say for example minutes) in order to be sure that all of the absorbed fuel is cleared out of the block I0 while this block is still warm. These timing operations are controlled by a timing mechanism con.- tained in a control box 92. This box can be located in any accessible place in the plane or mounted on the heater and is connected to the heater by the cable 9%. Power-is connected to this box by the conduit connection indicated at 90 and ordinarily this connection will be made at the main bus bar of the electrical system of the plane. Ordinarily this supplies current at a pressure of approximately 24 volts when the engines are not running and supplies the power directly from the generator at a pressure of about 28 volts during flight conditions. (in the face of the control box 82 is a starting indicator 98; which is moved 120 in a clockwise directionwhen the device is started. A push button i0ii is used for stopping the'operation of the furnace. The particular construction of this control box is not part of my invention. but'is made and offered for sale by others. Accordingly, its detailed construction is not shown. However the functional operation of this device will later be described in" connection with the specific controls of my heater.

This is normally a closed circuit switch but is controlled by a bi-metallic element so that it opens the circuit to turn oil the heater if the temperature rises above a predetermined level.

The numeral iddindicates a diaphragm which is operated by the air pressure in the air inlet pipe 39 which is connected to the blower 38. When the fan of this blower is operating, the pressure in the air inlet will be negative (sub-atmospheric) bill when the plane is in flight and the usual ventilating system is working, a positive pressure will be developed in this air inlet and this pressure is conducted to the diaphragm switch I06 by a tube I00 to operate a throw-switch. At H0 is indicated a barometric control which supplies a butterfly valve in the pipe 42 so that as the plane rises and the air is rarefied, a controlled weight of air will be fed to the heater for combustion purposes. This is equal to about twic the weight of air supplied by the'fan at sea-level.

Therelationship of these controls and the timing of the mechanism is illustrated diagrammatically in Fig. 10.

When the indicator 98 (see Fig. 9) is turned its full limit of 120 in a clockwise direction, it winds a clockwork mechanismwhlch controls the ignition connections and also the ultimate purging operation whereby the air current through the ignition block is continued after the fuel is turned ofi.

In Fig. 10 the clockwork mechanism is represented by the wheel H2 and as this view is a diagrammatic view taken from the inside of the box,

this is wound by rotating it in an apparent coun-p,

tel-clockwise direction and'it rotates in an apparent clockwise direction when running. The shaft 0 rotates with the wheel H2 and this shaft also carries a. cam wheel II6. A second cam wheel H8 is mounted on a shaft I'20 which is tensioned lightly for clockwise rotationby a spring I22. The shafts H0 and I20 are not connected together but nevertheless they are moved together with a permissible play of 30 by action of the bar I 20 which is fastened to the cam wheel Ill; and enters a 30 slot in the cam wheel IIB.

In Fig. 10 the parts are shown in their at rest position before the burner is started into operation. When the wheel H2 is rotated counterclockwise 120 the pin I26 rides up on the cam surface T28 closing the blower control switch I30.

One arm of this switch is connected by the line I32 with a source of power here indicated as a generator H4 or alternatively a battery I36 as has already been described. When the airplane is grounded power is supplied from batteries or an auxiliary power plant. In flight it is supplied direct from the engine generators. However, for the sake of convenience the drawings here indicate the power as being drawn from the generator.

76 bring a pin M2 up onto the cam face I44.

, III. In the, meantime the cam wheel III has been rotated 120 so that the pin I" just rides up on the cam surface closing theswitches IQ! and I. Current from the line [It passes through the switch I. the line Ill and thence to the solenoid I68 and through the manual stop switch m to the line "I. Thence it flows through the high temperature limit switch I12 (which is normally closed) to ground. when the cam wheel "8 is thus rotated 120' in the counterclockwise direction, the armature'ill rotates with it and is heldby the solenoid I" so that earn wheel I is held stationary during the operating run.

Current from line I" not only passes through the solenoid Ill but also through the line I18, through the resistance Ill and through the fuel pressure switch It to the variable speed motor CI of the fuel pump it, and thence to ground. Since thiscurrent is passed through the greater ortion of the length of the resistance ill the fuel pump will be operated at a relatively low speed. Thus when the device is supplied with air by the blower 80 the fuel supply is maintained relatively low.

After the device is operated about 5 minutes the igniter is disconnected. This is. accompanied by the rotation of the cam wheel ill through the arc of 30' permitted by the movement of pin I24 in the slot of the cam wheel Hi This 30' movement permits pin I42 to ride of! of the cam face I, opening switch H6 and thereby disconnecting the igniter ll. At the same time that switch Ill opens. switch I" is closed so that current is supplied through the line ill to the line I" to compensate for the fact that switch I has been opened by the de-energising of solenoid I ll.

When the plane is in flight. air pressure will build up from the scoop in the inlet of the blower II and when this air pressure reaches a predetermined level it'operates the ram switch I to disconnect the blower 88. At the same time, the

switch throws over to'close the circuit from the line I" to a line I" which through switch I! and thence to line I which is tapp d onto an intermediate point of resistance ill so that a greater amount of current will reach the-motor fl and thereby increase the fuel flow to keep it in proper proportion to the increased flow of air that is entering from the air scoop. A fuel supply pilot light as (visible on the side of box 92) is also connected to line I" as a safety measure. By-passingthe resistance in is a circuit running v through the pump exciter button II]. This can be used when the device is first turned on so that momentarily the pump 'will be operated at hi h speed to bring up enough fuel to saturate the block. s

The fuel pressure switch II is so constructed -that if the fuel pressure between float valve M and the fuel pump it rises too high, the fuel pressure switch 8 will open thereby cutting of! the fuel pump until the pressure returns to normal. In view of the fact that the battery I ordinarily supplies current at a lower voltage than generator I, a battery switch III is. supp ed to bY-pass a portion of resistance "8 when running on the batteries. As soon as the generators start operating this switch should be opened.

12 To shut off the burner, the manual stop swi ch m is opened (and the same effect will be has if the high temperature limit switch i1: should open). This will stop the flow of power through the solenoid I and release the armature ill which will immediately permit off of cam surface ill, opening both switches I82 and I so that the fuel pump will be disconnected and stop operating. It will be noted thatcam wheel II will still have a 90 angle to pass through before it comes to rest, which takes about 15 minutes, and it is only at the end of this period hat pin I28 will drop'ofl of cam face I28. Durin this time, the circuit will be maintained through switch I" and lines In and "I so that the blower II will remain in operation if the movement of the plane is not supplying sufficient air to keep open the ram switch that runs to the blower. This will insure a movement of air through the block ll for an appreciable time after flow of fuel into this block is stopped and this will mean that all fuel that has been soaked up by the block will be driven out and burned so that .the'block will be left dry until it is desired a ain to start up the burner.

Incidentally I may point out that the device operates quite successfully when thecasing or container which holds the capillary block (such as the casing designated by the numeral in the example) is made with an enlarged opening on both sides of the block instead of having separate perforations to correspond with the air passages as shown in this specific example. I have also found that if the casing is sufficiently protecteg from the heat so that it does not rise to a temperature substantially above the temperature of the preheated air, the fuel can simply be fed into this casing and it is not necessary to feed it into the interior of the porous block as illustrated in the example.

when using burners of this general type in small sizes, as for heating automobiles or trucks, the action can be much more rapid than that which has been indicated above. For example, I have found that with the small type of burner I the ignition cut-off can be taken care of by the use of a bi-metallic element so constructed that the ignition will cut off in about 30 seconds after the flame is initiated. Also with these small types of burners employing gasoline as a fuel, the purging can be accomplished in as short a time as one minute.

It is understood that the example given is intended only by way of illustration in order to explain the best mode in which I have contem- I plated applying the principles explained in the earlier part of my application and is not intended as a limitation, since the improvements and combinations which I claim to be my invention are set forth in the appended claims,-

What I claim is:

1. In an oil burner, the combination of a heatresistant porous block having air passages through it, means for delivering liquid fuel to be absorbed by such block,' an enclosure for the block largely covering the surfaces of such block other than the surfaces through which the ends of such passage run to prevent fuel being volatilized and burned around and against the perlphery of the block, means for forcing air through the passages in-the block at a velocity adapted to prevent combustion within the block, means for forming a mixing zone into which such passages discharge vaporized fuel and air, means for admitting'secondary air into such mixing pin III to drop 13' none, means forming a combustion chamber in whichthe iuel' mixture is burned, a heat exchanger communicating with the combustion chamber and including means whereby oombus-- tion air is preheated by the products oi combustion, said air preheating means being so proportioned that when the furnace is operating efiiciently such combustion air will be preheated to a temperature of at least 150' 1"., means forming a chamber on'the inlet side of the block and means for admitting said preheated combustion air into such chamber at a temperature of between 150 1". and 400' I". to supply the heat units necessary for. volatilising iuel within said block.

2. A structure as specified in claim 1 in which the admitting means for the secondary air is conangers structed to,- admit air into the mixing zone at points removed from the face 0! the block. .3. A structure as specified in claim 1 in which the enclosure for the porous block includes a cliplike structure with the air passages above such cup-like structure and means is provided so that the liquid oillevel will not rise above the upper edge 01 the cup-like structure.

4. The combination of a heat-resistant porous block having passages through it. an enclosureior the block-largely covering the surface oi the block other than the suriaces through which the ends oi such passages run, a pipe to conduct oil to the block within such enclosure. a sleeve extending irom'the discharge end of the block to form 'a mixing zone into which such passages discharge vapor-ind fuel and air, openinn in such sleeve for admitting secondary into the mixing none, means iorming a combustion chamber in which the final mixture is burned, means forming a header chamber on the inlet side oi the block, a heat exchanger communicating with the combustion chamber and including a pipe running therethrough and opening into said header chamber for preheating air conducted to the burner, said pipe being so proportioned that the air passing through it will be heated to a temperature oi between 150' 1". and 400 1''. to supply the heat units necessary for volatilizing fuel within said block and means including a ran for forcing air through said pipe and then through said block at a highenough velocity to prevent combustion within theblock.

rmco mms n. m.

, anrnnnucns crren 2,388,746 Hess 

